1. Field of the Invention
The present invention relates generally to spinal implantations and in particular to a dynamic stabilization device configured for the spine.
2. Description of Related Art
Methods of spinal stabilization have previously been proposed. Previous methods have incorporated various components configured to provide some type of flexibility. Jahng et al. (U.S. patent number 2005/0203513) teaches a spinal stabilization device. The stabilization device includes a longitudinal member having first and second ends as well as a flexible section disposed between the first and second ends. Jahng further teaches a cross sectional profile for the flexible section that is different than the cross sectional profiles of the first and second ends. Jahng teaches a flexible section that includes spiral cut grooves to improve flexibility.
Generally, spiral cut grooves may not provide the same degree of flexibility and support as a spring. Methods of spinal stabilization including screws have also been proposed. Timm et al. (U.S. patent number 2005/0171543) is directed to a system for effecting multi-level spine stabilization. Timm teaches a system including a plurality of pedicle screws that are joined by rods. Timm further teaches that at least one of the rods includes a dynamic stabilizing member. Timm teaches an inner first spring and an outer second spring. In the Timm design, the inner first spring is generally disposed within the outer second spring. Timm teaches springs that are not connected directly to the stabilization device at their ends, but instead are free springs disposed between two surfaces.
Colleran et al. (U.S. patent number 2006/0036240), teaches a system and method for dynamic skeletal stabilization. Colleran teaches two screws that are each associated with a separate bracing portion. Colleran teaches a spring and two stops that allow the two bracing portions to move longitudinally with respect to one another. This provides some degree of movement between the two screws. In the Colleran design, one of the brace portions may also bend.
Rothman et al. (U.S. patent number 2006/0229612) teaches a method for vertebral stabilization using sleeved springs. Rothman teaches a spring that is disposed between two anchoring elements. Rothman further teaches sleeve elements that cover the ends of the springs. The sleeve elements include an inner surface configured to receive the springs and an outer surface configured to engage the anchoring elements. The sleeve elements include ends that serve as stops for the spring.
These methods and systems incorporating springs as dynamic components have several drawbacks. First, the methods and systems taught here lack well defined connection points for the springs, and instead rely on stops or sleeve assisted stops. Also, in these systems, the springs may not facilitate inward tension as the springs are stretched, nor facilitate outward tension that is associated with spring compression.
Methods of attaching rods to bone screws have been previously proposed. Tornier et al. (U.S. Pat. No. 5,662,651) teaches an external or internal fixator for repairing fractures of arthroplasties of the skeleton. Tornier teaches an implant screw that is connected to a support that is angularly indexed with respect to the screw. The support includes a cavity configured to receive a connecting rod. Tornier further teaches a locking screw that is fastened into place into the support member, thereby locking the connecting rod into place. The Tornier design has several drawbacks. The connecting rod is attached to a support that is separate from the screw, providing a potentially weakened connection between the connecting rod and the screw. Additionally, the locking screw does not include provisions to easily receive the surface of the connecting rod. Furthermore, Tornier does not teach a drive receiving surface used to install the screw.
There is a need in the art for a design that solves many of the problems of the prior art.